U.S. patent number 4,673,855 [Application Number 06/706,501] was granted by the patent office on 1987-06-16 for restraining the instability of a stepper motor.
This patent grant is currently assigned to Sodeco-Saia AG. Invention is credited to Pierre Boillat.
United States Patent |
4,673,855 |
Boillat |
June 16, 1987 |
Restraining the instability of a stepper motor
Abstract
In an apparatus and method for preventing instability of a
stepper motor operated by a plurality of alternating currents of
different respective phases and controlled by a sequence of control
pulses, the control pulses defining an angular parameter of the
stepper motor, the steps include determining the sum of the phase
currents, transforming the sum of the phase currents into a voltage
fluctuating about an average value, determining the average
voltage, and thereafter feeding back the fluctuating voltage so as
to angle-modulate said control pulses.
Inventors: |
Boillat; Pierre (Meyriez,
CH) |
Assignee: |
Sodeco-Saia AG (Murten,
CH)
|
Family
ID: |
4291654 |
Appl.
No.: |
06/706,501 |
Filed: |
February 28, 1985 |
Foreign Application Priority Data
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Nov 6, 1984 [CH] |
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05323/84 |
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Current U.S.
Class: |
318/696;
318/685 |
Current CPC
Class: |
H02P
8/00 (20130101); H02P 8/40 (20130101); H02P
8/34 (20130101); H02P 8/32 (20130101) |
Current International
Class: |
H02P
8/32 (20060101); H02P 8/40 (20060101); H02P
8/34 (20060101); H02P 8/00 (20060101); H02P
008/00 () |
Field of
Search: |
;318/696,685
;307/265 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
0036931 |
|
Oct 1981 |
|
EP |
|
117776 |
|
Jan 1975 |
|
DE |
|
2705758 |
|
Oct 1981 |
|
DE |
|
Other References
"Solid State Electronic Circuits for Engineering Technology",
Anthony S. Manera, McGrow-HIll, 1973. .
Landis & Gyr Mitteilungen 31, 1984, pp. 28-35. .
Wetter, "Amortissement des Oscillations d'un moteur pas a pas",
SEV/VSE 73, 1982, pp. 527-534..
|
Primary Examiner: Shoop, Jr.; William M.
Assistant Examiner: Bergmann; Saul M.
Attorney, Agent or Firm: Marmorek, Guttman &
Rubenstein
Claims
Having thus described the invention, what I claim as new and desire
to be secured by Letters Patent is as follows:
1. In an apparatus for preventing instability of a stepper motor
operated by a plurality of alternating currents of different
respective phases and controlled by a sequence of control pulses,
said control pulses defining an angular parameter of the stepper
motor,
the improvement comprising
a timing generator for producing a pulse signal,
a combined controllable delay element and pulse generator connected
to the output of said timing generator, and operable to pulse time
modulate said pulse signal,
a sequence generator connected to the output of said combined
controllable delay element and pulse generator, said sequence
generator generating said control pulses, said control pulses
controlling said stepper motor,
a resistor connected to an output of said sequence generator for
providing the sum of said phase currents, and for transforming said
sum into a voltage fluctuating about an average value,
a low-pass filter connected to said resistor for receiving said
voltage, and for determining said average value with a
substantially 90.degree. phase shift, and
a high-pass filter connected to an inut of said combined delay
element and pulse generator for providing fluctuations about said
average value to said combined delay element and pulse generator
for pulse time modulating said pulse signal, said combined delay
element and pulse generator including a counter, a high frequency
pulse generator connected to an input of said counter, an
analog-to-digital converter having an output thereof connected to
another input of said counter, and a decoder having an input
thereof connected to an output of said counter.
2. The apparatus as claimed in claim 1, wherein said decoder
includes a NAND gate.
3. The apparatus as claimed in claim 1, further including an
amplifier having an input thereof connected to an output of said
low-pass filter, and having an output thereof connected to an input
of said high-pass filter.
4. The apparatus as claimed in claim 1, wherein said low-pass
filter and said high-pass filter are connected to one another so as
form a band-pass filter.
Description
BACKGROUND OF THE INVENTION
The invention relates to a method to cure the instability of a
stepper motor and to a device to implement the method with the aid
of a feedback signal which controls an angular parameter of control
impulses of the stepping motor. Stepper motors are employed, for
example, in printers, machines for generating drawings,
floppy-drivers, hard disc-drivers and the like. From U.S. Pat. No.
4,091,316 there is known a method and a device to avoid
oscillations and any loss of synchronism of stepper motors while
using a tacho-alternator for providing an actual value, and a
control circuit for regulation, namely modulation of the phase
angle of the control impulses of the stepper motor.
SUMMARY OF THE INVENTION
It is an object of the invention to devise a method and implement
the method which permits:
driving of single-phase or multi-phase stepping motors, and any of
their coupling elements, without the employment of any sensors,
such as, for example, Hall element sensors, induction coils,
expensive tacho-alternators, mechanical or optical sensors, in a
stable manner within their parametric resonance bands, and wherein
the stabilization is relatively rapid and independent of any load
and any dead time, namely easily tolerates load changes in the
range from one to one hundred;
proper operation at an extremely large velocity range from zero to
35,000 revolutions per minute;
improvement of the output or effectivity of a stepper motor at a
high output and so permit high mechanical effectivity;
operation independent of the type of sequence generator used, for
example use of a constant voltage control, of a constant current
control, of a chopper control of a bi-level control, or of a
left/right control;
stabilization of the stepper motor both during uniform movements,
as well as during accelerated movements;
cost at a price which has a reasonable relation to the cost of a
stepper motor;
driving of two or of several stepper motors connected in parallel
by means of a single stabilization device.
This makes it frequently possible to use smaller or less expensive
stepper motors, and/or to utilize such stepper motors for purposes
in which it has hitherto only been possible to use direct current
motors for stable operation.
The stabilizing device should, if possible, be so implemented, that
it can be used as an interface circuit between constructional
elements of a control device of a stepper motor which are already
available, without the control device having to be modified to a
large extent.
This object is attained by an apparatus and a method for preventing
instability of a stepper motor operated by a plurality of
alternating currents of different respective phases, and controlled
by a sequence of control pulses, the control pulses defining an
angular parameter of the stepper motor, which includes determining
the sum of the phase currents, transforming the sum of the phase
currents into a voltage fluctuating about an average value, and
thereafter feeding back the fluctuating voltage so as to
angle-modulate said control pulses.
BRIEF DESCRIPTION OF THE DRAWING.
For a fuller understanding of the nature and objects of the
invention, reference should be had to the following detailed
description, taken in connection with the accompanying drawings, in
which:
FIG. 1 is a block schematic diagram of a first version of the
device to avoid instability of a stepper motor;
FIG.2 is a block schematic diagram of a second version of such a
device;
FIG. 3 is a block schematic diagram of a third version of such a
device;
FIG. 4A through 4D are characteristic lines of different respective
control signals of a stepper motor as s function of time, when
using phase modulation;
FIG. 5 are characteristic lines of the torque and of the mechanical
output of a stepper motor as a function of the stepping velocity,
both when stabilization is present, and when it is not present;
FIG. 6 is a block schematic diagram of a controllable delay element
having an analog comparator; and
FIG. 7 is a block schematic diagram of a combination of a
controllable delay element and of a pulse shaper having a
synchronous digital circuit.
The same reference numerals denote idential parts in all FIGS. of
the drawing.
DESCRIPTION OF THE PREFERRED EMBODIMENTS.
Referring now to the drawing, each device shown in FIGS. 1-3 shows
at least:
A stepper motor 1, fed by a source of D.C. voltage U;
A sequence generator 2;
A measurement resistor 3;
A low-pass filter 4;
Optionally an amplifier 5;
A high-pass filter 6; and
A pulse or timing generator 7.
Components which are only optinally present are shown dotted in
FIGS. 1-3.
The stepper motor 1 has an arbitrary number of phases. In the
drawings the presence of a four-phase stepper motor 1 has been
assumed. In that case the sequence generator 2 has four outputs
connected to the stepper motor 1, which are, for example, open
collector outputs. In that case the output driver of the sequence
generator 2 consists in the case illustrated of four bipolar
transistors T1, T2, T3 and T4, whose collectors, in turn, form the
four outputs of the sequence generator 2, and whose base
connections are connected to the four respective outputs of a
sequence control circuit 8; the input of the sequence control
circuit 8 is also the input of the sequence generator 2. The
emitters of the four bipolar transistors T1, T2, T3, and T4 are,
for example, connected within the sequence generator 2 with one
another. Such sequence generators are known per se and are
obtainable in commerce.
The terminal of the D.C. voltage U, which is not connected to the
stepper motor 1 is not illustrated, but is, for example, connected
to ground. In that case a first terminal of the measurement
resistor 3 is also connected to ground.
All devices which are illustrated in FIGS. 1-3 are connected to one
another in a unipolar manner:
The emitters of the bipolar transistors T1, T2, T3 and T4 are
connected with the second terminal of the measurement resistor 3,
and with the input of the low-pass filter 4;
The output of the low-pass filter 4 is connected with the input of
the amplifier 5, or if the input to the amplifier 5 is not
available, are connected with the input of the high-pass filter 6;
and
The output of the amplifier 5, if available, is connected with the
input of the high-pass filter 6.
In the version shown in FIG. 1, the following are further connected
to one another in a unipolar manner:
The output of the high-pass filter 6 is connected with a voltage
controlled input of the tact or timing generator 7; and
The output of the timing generator 7 is connected with the input of
the sequence generator 2.
In the version shown in FIG. 2 there are additionally present:
A controllable delay element 9; and
Optionally an impulse former or pulse shaper 10; and
wherein the following elements are connected to one another in a
unipolar manner:
The output of the high-pass filter 6 is connected with a control
input of the delay element 9;
The output of the tact or timing generator 7 is connected with the
input of the delay element 9;
The output of the delay element 9 is connected with the input of
the impulse former or pulse shaper 10, or, in the event the impulse
former 10 is not available, the output of the delay element 9 is
connected with the input of the sequence generator 2; and
The output of the impulse former or pulse shaper 10, if it is
available, is connected with the input of the sequence generator
2.
In the version shown in FIG. 3, in addition to the version shown in
FIG. 2, there is present a frequency/voltage transducer 11, and
wherein the following are additionally connected with one
another:
The output of the tact or timing generator 7 is connected with the
input of the frequency/voltage transducer 11; and
The output of the frequency/voltage transducer 11 is connected to a
further control input of the delay element 9. The pulse of timing
generator required inversions 2 and 3 (see FIGS. 2 and 3) is a
simple generator of rectangular pulses, for example an astable
multivibrator, while the pulse generator used in the version of
FIG. 1 is required to be a voltage-controlled generator of
rectangular pulses, for example, an astable multivibrator
constructed by means of a timer of the type LM 556. The timer of
the type LM 556 is, for example, obtainable from National
Semiconductor Corp. 2900 Semiconductor Drive, Santa Clara,
California 95051, and is described in their "Lineardata book" 1978,
as well as in their "Linear applications Handbook" 1978.
The high-pass filter 6 and the low-pass filter 4 are, for example,
known L-RC elements, and wherein in the high-pass filter 6 there is
arranged a capacitor in the longitudinal branch, and a resistor in
the transverse branch; however in the low-pass filter 4, in a
reverse manner, the capacitor is arranged in the transverse branch,
and the resistor in the longitudinal branch. In the simplest case
the high-pass filter 6 consists only of a capacitor, and wherein a
terminal of this capacitor forms the input of the high-pass filter
6, while the other terminal of the capacitor forms an output of the
high-pass filter 6. In the event the amplifier 5 is not available,
the high-pass filter 6 can be combined with the low-pass filter 4
so as to be connected in series, and thus form only a single
bandpass filter.
The controllable delay element 9 (see FIGS. 2 and 3) is, for
example, a monostable multivibrator, which is constructed by means
of a timer of the type LM 556. But it can also be constructed as
shown in FIGS. 6 and 7. The impulse former or pulse shaper 10,
which is, for example, a known monostable multivibrator controlled
by negative going edges, and which is available in commerce, is
only required if the sequence generator 2 is impulse-controlled. If
the sequence generator 2 is, however, controlled by pulse edges or
if the circuit shown in FIG. 7 is used, then the impulse former or
pulse shaper 10 can be omitted. The frequency/voltage transducer 11
(see FIG. 3) can, for example, be constructed with the aid of a
timer of the type LM 122 of the National Semiconductor Corp., which
is also described in the already stated publications.
FIG. 4A represents the characteristic line of the alternating
voltage portion of the average value of the sum of all phase
currents of a stepper motor 1 as a function of time. For
simplicity's sake it was shown in FIG. 4A as a sinusoidal
curve.
FIG. 4B represents the characteristic line of the output signal of
the pulse or timing generator 7 as a function of time. It consists
of a sequence of rectangular impulses of a duration .tau. and has a
period T=1/f, wherein f is the tact or timing frequency. T is, for
example, equal to 1 ms.
FIG. 4C is a characteristic line of the output signal of the delay
element 9 as a function of time. It consists of a sequence or
rectangular impulse-duration modulated impulses having a period T.
T.sub.1 is the delay time of the delay element 9, if the
alternating voltage part of the average value of the sum of the
phase currents namely the modulation, is equal to zero.
FIG. 4D represents the characteristic line of the output signal of
the impulse former or pulse shaper 10 as a function of time. It
consist of a sequence of rectangular impulses having a duration
.tau., whose positive-going edges coincide in time with the
negative-going edges of the impulse shown in FIG. 4C.
Advantageously the value of the delay time T.sub.1 of the delay
element 9 is selected at zero modulation, namely at the zero value
of the error-correction signal at the output of the high-pass
filter in FIGS. 2 and 3 in such a manner, so that the impulses
shown in FIG. 4D, or the negative-going edges of the impulses shown
in FIG. 4C lie time-wise approximately in the center between two
consecutive impulses of the output signal of the tact or timing
generator shown in FIG. 4B; this means that T.sub.1 is selected to
be approxaimately equal to T/2. The impulse duration .tau. and the
impulse duration .tau..sub.1 are selected to be significantly
smaller than the delay time T.sub.1.
In FIG. 5 there are shown four characteristic lines M.sub.0,
M.sub.1, P.sub.0 and P.sub.1 as a function of the step velocity of
the stepper motor 1. The characteristic line M.sub.0 represents the
torque of a stepper motor 1 without any stabilization, M.sub.1
represents the torque in the presence of stabilization, P.sub.0
represents the mechanical output of the stepper motor 1 without any
stabilization, and P.sub.1 its output in the presence of
stabilization.
The characteristic torque line M.sub.0 suffers a collapse of
torque, for example at a velocity of about 1000 steps per second,
and the output characteristic line P.sub.0 has a maximum value
below 1000 steps per second, which is significantly smaller than
the maximal value of the output characteristic line P.sub.1, which
lies above 1000 steps per second. The characteristic line M.sub.1
of the torque decreases continuously without any collapse with an
increasing step velocity v.
The controllable delay element 9 shown in FIG. 6 consists of a saw
tooth generator 12 and an analog comparator 13, whose minus input
forms a control input, and whose output forms the output of the
delay element 9. The output of the saw tooth generator 12 is
connected with the plus input of the comparator 13, and its input
forms the input of the delay element 9.
The combination 9;10 of a delay element and of a pulse shaper shown
in FIG. 7 consists of a high-frequency pulse generator 14, a
counter 15, analog-to-digital converter or transducer 16, and a
decoder 17; the output of the decoder 17 forms the output of the
combination 9;10. The control input of the delay element 9
controlled by the high-pass filter 6 according to FIG. 2 or FIG. 3
is equal to the control input of the combination 9; 10 and is
formed by the analog input of the analog/digital transducer 16; the
digital output of the analog/digital transducer 16 is connected
with the aid of a bus connection with the parallel input of the
counter 15. The output of the high frequency tact generator 14 is
connected to the timing input of the counter 15, whose load input
forms the input of the combination 9; 10; that input is controlled,
according to FIG. 2 or FIG. 3, by the timing generator 7. The
parallel output of the counter 15 is connected through a further
bus connection with the input of the decoder 17, which, for
example, consists of a NAND gate, which has as many inputs as the
binary counter 15 has parallel outputs. The counter 15 may also be
a binary counter or a decade counter.
Operation
Abrupt losses of torque occur in stepper motors within a region of
high velocities at certain critical frequency regions. The stepper
motor may fall out of synchronism and may stop. This behavior can
be explained by parametric resonances of the stepper motor, as a
rotor of the stepper motor, in addition to rotating at a constant
angular velocity, executes oscillations; the amplitudes of these
oscilations increase severely in these critical frequency regions
and may become so severe, that the stepper motor loses its
synchronism and stops.
The stepper motor is characterized by its torque. In the absence of
any stabilization its torque characteristic line within the
frequency region from 0 to 20 kH.sub.0 theoretically suffers
several collapses; in practice, however, it suffers at least one
collapse, which occurs at approximately at 1000 steps per second,
as is shown in FIG. 5 by the characteristic line M.sub.0 (the
so-called "pull out" region). This results in the stepper motor
being able to be driven in the absence of any stabilization only at
a low velocity, for example below a 1000 steps per second, namely
in a velocity region in which its mechanical output according to
the characteristic line P.sub.0 of FIG. 5 is relatively low, and
its power and efficiency is poor.
Proposals for stabilizing of a stepper motor which requires sensors
or couplings cannot be used, as a rule for reasons of price and/or
space utilization. A tacho-alternator, for example, costs a
multiple of the price of a low cost stepper motor, for example that
of a "tin can" stepper motor. Furthermore, as a rule no space is
available for space-consuming couplings. In the inventive device
the stepper motor itself is used as a sensor for determining an
actual value, and therefore for determining an error correction
signal of a control circuit. It is not the deviation of the
velocity from a desired velocity, which is used as an
error-correcting signal, as is the case in the state of the art,
but the oscillations of the load angle about its nominal load angle
are used as an error-correction signal. This has, inter alia, the
advantage that the stabilization of the stepper motor is
independent of any load.
During stable operation of the stepper motor, and at a given load
the envelope of its phase current, and therefore also its average
value is approximately constant. During unstable operation,
however, oscillations of the envelope curve result, and
consequently also of the average value of the phase current, which
are a measure for the oscillation of the load angle around its
nominal value.
In all three versions shown in FIGS. 1-3 the instability of a
stepper motor 1 is avoided with the aid of a feedback signal, which
modulates an angular parameter of the control impulses of the
stepper motor 1, by the algebraic sum current of the phase current
of the stepper motor 1 being continuously determined with the aid
of the measuring resistor 3 and transformed into a proportional
voltage whose average value is then generated with the aid of the
low-pass filter 4. As the individual phase currents of the stepper
motor 1 occur time-wise approximately sequentially, the voltage
across the measuring resistor 3 is approximately proportional to
the instantaneously passing phase current of the stepper motor 1,
while the oscillations of the average value obtained with the aid
of the low-pass filter 4 are a measure for the oscillations of the
load angle of the stepper motor 1. The fluctuations of this average
value, which may have a frequency from 0 to 400 Hz, are independent
of the average value, and therefore also independent of the nominal
load angle. An advantage of the use of fluctuations of this average
value as an error-correction signal lies therein, that it reaches
its maximal value shortly before the stepper motor 1 reaches its
critical point, namely before the stepper motor 1 loses
synchronism; at that time the load angle is maximal. This is in
contrast to the state of the art, based on velocity, where the
actual velocity value at that moment in time is equal to
.omega.0=2.pi.SPS/SPR, where SPS=step per sec. and SPR=step per
revolution, therefore giving no error signal.
The value of the output signal of the low-pass signal 4 depends in
all three versions on the value of the measurement resistor 3, and
on the value of the phase currents. It is, as a rule, 100 to 1000
times smaller than the D.C. voltage U, which feeds the stepper
motor 1. If the value of the output voltage of the low-pass filter
4 is insufficient to drive the following control circuit, then an
amplifier 5 is interconnected between the low-pass filter 4 and the
high-pass filter 6. The amplifier 5 is an alternating-current
amplifier, and amplifies the alternating voltage portion, namely
the fluctuations of the average value, or, in the versions 2 and 3,
the fluctuations of a phase-displaced average value, before these
fluctuations modulate the control impluses of the stepper motor
1.
The following high-pass filter 6 eliminates, in the absence of an
amplifier 5, the D.C. voltage component of the average value, and
in the presence of the amplifier 5, its output "offset voltage, so
that in any case, only the possibly amplified fluctuations of the
average value are determined, which subsequently reach the voltage
control input of the timing generator 7 (see FIG. 1), or the
control input of the delay element 9 (see FIGS. 2 and 3), so that
the control impulses of the stepper motor 1 are angle
modulated.
In the first version shown in FIG. 1, the modulated angular
parameter is the frequency of the control impulses. The alternating
current portion of the optionally amplified average value changes
in this version the frequency of the rectangular pulse signals
generated by the timing generator 5 continuously, so that the
following sequence generator 2 is fed with frequency-modulated
rectangular impulses. The low-pass filter 4 and the high-pass
filter 6 generate per se a small phase displacement of the
alternating voltage portion of the average value. In the version 1
both those filters are, however, dimensioned in a known manner in
such a way that any phase displacement generated by them are as
small as possible, so that the alternating voltage portion of the
average value frequency-modulates the control impulses generated by
the timing generator 7, and subsequently by the sequence generator
2, without any additional phase displacement occurring. Shortly
before the stepper motor 1 reaches its critical point, the effect
of the frequency modulation on the control impulses generated by
the sequence generator 2 of the stepper motor 1 is largest, so that
the corrective effect of the control circuit is also maximal, and
therefore counteracts most strongly any loss of synchronism of the
stepper motor 1, as far as regulatory control is concerned.
In the versions 2 and 3 shown in FIGS. 2 and 3 the modulated
angular parameter represents the phase of the control impulses. In
these versions the control impulses of the stepper motor 1
generated by the sequence generator 2 are phase modulated. As it is
well known that a frequency is proportional to d.phi./dt, wherein
.phi. is a phase, and as it is known that the derivative causes a
phase rotation of 90 degrees, the average value, according to FIG.
1, must be additionally phase-shifted by 90 degrees when phase
modulation is used, namely in versions 2 and 3, before its
fluctuations phase modulate the control impulses of the stepper
motor 1. This is accomplished in a simple and elegant manner, by
the phase displacement caused by the low-pass filter 4 being
selected by means of dimensioning of the low-pass filter 4, --which
is known per se, --being not made as small as possible, but being
made as equal to 90 degrees as possible. The error-correction
signal at the output of the high-pass filter 6 then has the
required phase position needed for the phase modulation. The
error-correction signal then shifts the delay times generated by
the delay element 9 (see FIG. 4C), namely the impulse duration of
its monostable multivibrator, so that, for example, all
positive-going edges of the rectangular impulses generated by the
timing generator 7 (see FIG. 4B) appear delay-phase modulated as
negative-going edges at the output of the delay element 9 (see FIG.
4C). If the following sequence generator 2 is only edge-controlled,
then the output signal of the delay element 9 can control the
sequence generator 2 directly. Otherwise, the negative-going edges
of the output signal of the delay element 9 must be conditioned
with the aid of the pulse shaper 10, and be transformed into
impulses, before they can be fed to the following sequence
generator 2. The pulse shaper 10 therefore associates each
negative-going edge of its input signal with an impulse of constant
duration .tau..sub.1 (see FIG. 4D).
So as to obtain a maximal control both in a positive and in a
negative phase direction, the delay time T.sub.1 of the delay
element 9 is so selected, that in the case of an error-correction
signal zero at the output of the high-pass filter 6 and
controlling, for example, negative-going edges at the output of the
delay element 9 occur time-wise approximately in the center between
two consecutive output impulses of the timing generator 7. So as to
always automatically obtain this effect at variable control
frequencies of the stepper motor 1, namely at variable frequencies
of the timing generator 7, the average value of the delay time of
the delay element 9, namely the delay time T.sub.1, is adjusted to
a time-wise approximately center position between two succeeding
output pulses of the timing generator 7 at a zero value of the
error-correction signal in the version 3 (see FIG. 3) with the aid
of the output signal of the frequency/voltage transducer 11. The
output signal of the frequency/voltage transducer 11 is
proportional to the frequency of the output signal of the timing
generator 7, and therefore inversely proportional of the timing
generator 7, and therefore inversely proportional to its period T,
namely to the distance between two consecutive output pulses of the
timing generator 7 (see FIG. 4B).
The versions 2 and 3 shown in FIGS. 2 and 3, respectively, have the
advantage that the timing generator 7 need not be
voltage-controlled. A timing generator 7 not controlled by any
voltage, as well as a sequence generator 2, and a measurement
resistor 3 are, as a rule, already present when stepper motors are
used, so that in this case the use of one of the two versions 2 and
3 has the advantage that only a simple interface circuit 18 need be
connected between the already available timing generator 3 and the
also already available combination 2;3 of the sequence generator 2
and of the measurement resistor 3, so as to remedy the instability
of the stepper motor 1 during operation. This interface circuit 18
consists, in the case of version 2, (see FIG. 2) of a low-pass
filter 4, optionally of an amplifier 5, of a high-pass filter 6, of
a delay element 9, and optionally of the pulse shaper 10. In the
case of the version 3 (see FIG. 3) optionally the frequency/voltage
transducer 11 could be added.
The delay element 9 shown in FIG. 6 operates as follows: the
saw-tooth generator 12 transforms the rectangular output pulses of
the timing generator 7 into saw-tooth impulses, which change the
state of the analog comparator 13, whenever their value reaches the
value of the error-correction signal available at the control input
of the delay element 9. The duration of the rectangular impulses
appearing at the output of the comparator 13 is therefore
proportional to the error-correction signal and is therefore
impulse modulated thereby exactly as is the case in the
controllable monostable multivibrator.
In the analog-to-digital transducer 16 of the circuit 9;10 shown in
FIG. 7 the analog error-correction signal supplied by the high-pass
filter 6 is changed into a digital value, and this value is loaded
by each output impulse of the timing generator 7, which appears at
the input of the circuit 9;10, into the counter 15. The counter 15
then counts, starting from this digital value, backwards the output
pulses of the high-frequency pulse generator 14. As soon as the
count value reaches the value zero, there appears at the output of
the NAND gate, forming the decoder 17, a short impulse for the
duration of the output impulse of the high-frequency pulse
generator 14, whose timing position, in turn, is proportional to
the digital value loaded into the counter 15, and is consequently
proportional to the error correction signal. The output pulses of
the circuit 9;10 are therefore phase modulated by this error
correction signal. A pulse shaper 10 is not required in this case,
as the conditioned pulses are automatically generated by the
circuit 9;10.
I wish it to be understood that I do not desire to be limited to
the exact details of construction shown and described, for obvious
modifications will occur to a person skilled in the art.
* * * * *